A team of researchers from Denmark has solved one of the biggest challenges in making effective nanoelectronics based on graphene. The new results have just been published in Nature Nanotechnology.
For 15 years, scientists have tried to exploit the “miracle material” graphene to produce nanoscale electronics. On paper, graphene should be great for just that: it is ultra-thin – only one atom thick and therefore two-dimensional, it is excellent for conducting electrical current, and holds great promise for future forms of electronics that are faster and more energy efficient. In addition, graphene consists of carbon atoms – of which we have an unlimited supply.
In theory, graphene can be altered to perform many different tasks within e.g. electronics, photonics or sensorssimply by cutting tiny patterns in it, as this fundamentally alters its quantum properties. One “simple” task, which has turned out to be surprisingly difficult, is to induce a band gap – which is crucial for making transistors and optoelectronic devices. However, since graphene is only an atom thick all of the atoms are important and even tiny irregularities in the pattern can destroy its properties.
“Graphene is a fantastic material, which I think will play a crucial role in making new nanoscale electronics. The problem is that it is extremely difficult to engineer the electrical properties,” says Peter Bøggild, professor at DTU Physics.
The Center for Nanostructured Graphene at DTU and Aalborg University was established in 2012 specifically to study how the electrical properties of graphene can be tailored by changing its shape on an extremely small scale. When actually patterning graphene, the team of researchers from DTU and Aalborg experienced the same as other researchers worldwide: it didn’t work.
“When you make patterns in a material like graphene, you do so in order to change its properties in a controlled way – to match your design. However, what we have seen throughout the years is that we can make the holes, but not without introducing so much disorder and contamination that it no longer behaves like graphene. It is a bit similar to making a water pipe that is partly blocked because of poor manufacturing. On the outside, it might look fine, but water cannot flow freely. For electronics, that is obviously disastrous,” says Peter Bøggild.
Now, the team of scientists have solved the problem. The results are published in Nature Nanotechnology. Two postdocs from DTU Physics, Bjarke Jessen and Lene Gammelgaard, first encapsulated graphene inside another two-dimensional material – hexagonal boron nitride, a non-conductive material that is often used for protecting graphene’s properties.
Next, they used a technique called electron beam lithography to carefully pattern the protective layer of boron nitride and graphene below with a dense array of ultra small holes. The holes have a diameter of approx. 20 nanometers, with just 12 nanometers between them – however, the roughness at the edge of the holes is less than 1 nanometer, or a billionth of a meter. This allows 1000 times more electrical current to flow than had been reported in such small graphene structures. And not just that.
“We have shown that we can control graphene’s band structure and design how it should behave. When we control the band structure, we have access to all of graphene’s properties – and we found to our surprise that some of the most subtle quantum electronic effects survive the dense patterning – that is extremely encouraging. Our work suggests that we can sit in front of the computer and design components and devices – or dream up something entirely new – and then go to the laboratory and realise them in practice,” says Peter Bøggild. He continues:
“Many scientists had long since abandoned attempting nanolithography in graphene on this scale, and it is quite a pity, since nanostructuring is a crucial tool for exploiting the most exciting features of graphene electronics and photonics. Now we have figured out how it can be done; one could say that the curse is lifted. There are other challenges, but the fact that we can tailor electronic properties of graphene is a big step towards creating new electronics with extremely small dimensions,” says Peter Bøggild.
About the Center for Nanostructured Graphene
• Funded by the Danish National Research Foundation with a total budget of 100 million DKK for the ten-year period 2012 – 2022. It focuses on basic research, but all its research projects have long-term perspectives for applications.
• the team is also part of the Graphene Flagship, which with a budget of €1 billion represents a new form of joint, coordinated research on an unprecedented scale, and is Europe’s biggest ever research initiative. It is tasked with bringing together academic and industrial partners to take graphene from the realm of academic laboratories into society in the space of 10 years, thus generating economic growth, new jobs and new opportunities for Europe.
How to build a better Battery through Nanotechnology
PALO ALTO, CALIFORNIA (Note to Readers: This original article was published in 2016 May. Recent updates, News Releases and a YouTube Video have been provided)
On a drizzly, gray morning in April, Yi Cui weaves his scarlet red Tesla in and out of Silicon Valley traffic. Cui, a materials scientist at Stanford University here, is headed to visit Amprius, a battery company he founded 8 years ago. Amprius Latest News Release(December 2018)
It’s no coincidence that he is driving a battery-powered car, and that he has leased rather than bought it. In a few years, he says, he plans to upgrade to a new model, with a crucial improvement: “Hopefully our batteries will be in it.”
Cui and Amprius are trying to take lithium–ion batteries—today’s best commercial technology—to the next level. They have plenty of company. Massive corporations such as Panasonic, Samsung, LG Chem, Apple, and Tesla are vying to make batteries smaller, lighter, and more powerful. But among these power players, Cui remains a pioneering force.
Unlike others who focus on tweaking the chemical composition of a battery’s electrodes or its charge-conducting electrolyte, Cui is marrying battery chemistry with nanotechnology. He is building intricately structured battery electrodes that can soak up and release charge-carrying ions in greater quantities, and faster, than standard electrodes can, without producing troublesome side reactions. “He’s taking the innovation of nanotechnology and using it to control chemistry,” says Wei Luo, a materials scientist and battery expert at the University of Maryland, College Park.
“I wanted to change the world, and also get rich, but mainly change the world.”
In a series of lab demonstrations, Cui has shown how his architectural approach to electrodes can domesticate a host of battery chemistries that have long tantalized researchers but remained problematic. Among them: lithium-ion batteries with electrodes of silicon instead of the standard graphite, batteries with an electrode made of bare lithium metal, and batteries relying on lithium-sulfur chemistry, which are potentially more powerful than any lithium-ion battery. The nanoscale architectures he is exploring include silicon nanowires that expand and contract as they absorb and shed lithium ions, and tiny egg like structures with carbon shells protecting lithium-rich silicon yolks.
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Watch a YouTube Video on the latest Update from Professor Cui (November 2018). A very concise and informative Summary of the State of NextGen Batteries.
** Amprius already supplies phone batteries with silicon electrodes that store 10% more energy than the best conventional lithium-ion batteries on the market.
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Another prototype beats standard batteries by 40%, and even better ones are in the works. So far, the company does not make batteries for electric vehicles (EVs), but if the technologies Cui is exploring live up to their promise, the company could one day supply car batteries able to store up to 10 times more energy than today’s top performers. That could give modest-priced EVs the same range as gas-powered models—a revolutionary advance that could help nations power their vehicle fleets with electricity provided by solar and wind power, dramatically reducing carbon emissions.
Cui says that when he started in research, “I wanted to change the world, and also get rich, but mainly change the world.” His quest goes beyond batteries. His lab is exploring nanotech innovations that are spawning startup companies aiming to provide cheaper, more effective air and water purification systems. But so far Cui has made his clearest mark on batteries. Luo calls his approach “untraditional and surprising.” Jun Liu, a materials scientist at the Pacific Northwest National Laboratory in Richland, Washington, put it more directly: Cui’s nanotech contributions to battery technology are “tremendous.”
Making leaps in battery technology is surprisingly hard to do. Even as Silicon Valley’s primary innovation, the computer chip, has made exponential performance gains for decades, batteries have lagged. Today’s best lithium-ion cells hold about 700 watt-hours per liter. That’s about five times the energy density of nickel-cadmium batteries from the mid-1980s—not bad, but not breathtaking. In the past decade, the energy density of the best commercial batteries has doubled.
Battery users want more. The market for lithium-ion batteries alone is expected to top $30 billion a year by 2020, according to a pair of recent reports by market research firms Transparency Market Research and Taiyou Research. The rise in production of EVs by car companies that include Tesla, General Motors, and Nissan accounts for some of that surge.
But today’s EVs leave much to be desired. For a Tesla Model S, depending on the exact model, the 70- to 90-kilowatt-hour batteries alone weigh 600 kilograms and account for about $30,000 of the car’s price, which can exceed $100,000. Yet they can take the car only about 400 kilometers on a single charge, substantially less than the range of many conventional cars. Nissan’s Leaf is far cheaper, with a sticker price of about $29,000. But with a smaller battery pack, its range is only about one-third that of the Tesla.
Improving batteries could make a major impact. Doubling a battery’s energy density would enable car companies to keep the driving range the same while halving the size and cost of the battery—or keep the battery size constant and double the car’s range. “The age of electric vehicles is coming,” Cui says. But in order for EVs to take over, “we have to do better.”
He recognized the need early in his career. After finishing his undergraduate degree in his native China in 1998, Cui moved first to Harvard University and then to the University of California (UC), Berkeley, to complete a Ph.D. and postdoc in labs that were pioneering the synthesis of nanosized materials. Those were the early days of nanotechnology, when researchers were struggling to get a firm handle on how to create just the materials they wanted, and the world of applications was only beginning to take shape.
While at UC Berkeley, Cui spent time with colleagues next door at the Lawrence Berkeley National Laboratory (LBNL). At the time, LBNL’s director was Steven Chu, who pushed the lab to invent renewable energy technologies that had the potential to combat climate change, among them better batteries for storing clean energy. (Chu later went on to serve as President Barack Obama’s secretary of energy from 2009 to 2013.)
“At the beginning, I wasn’t thinking about energy. I had never worked on batteries,” Cui says. But Chu and others impressed on him that nanotechnology could give batteries an edge.
As Chu says now, it offers “a new knob to turn, and an important one,” enabling researchers to control not only the chemical composition of materials on the smallest scales, but also the arrangement of atoms within them—and thus how chemical reactions involving them proceed.
After moving to Stanford, Cui quickly gravitated to the nexus between nanotechnology and the electrochemistry that makes batteries work—and accounts for their limitations. Take lithium-ion rechargeable batteries. In principle, these batteries are simple: They consist of two electrodes divided by a membrane “separator” and a liquid electrolyte that allows ions to glide back and forth between the electrodes.
When a battery is charging, lithium ions are released from the positive electrode, or cathode, which consists of a lithium alloy, commonly lithium cobalt oxide or lithium iron phosphate. They are drawn toward the negatively charged electrode, called the anode, which is usually made of graphite. There they snuggle in between the graphite’s sheets of carbon atoms. Voltage from an external power source drives the whole ionic mass migration, storing power.
When a device—say, a power tool or a car—is turned on and demands energy, the battery discharges: Lithium atoms in the graphite give up electrons, which travel through the external circuit to the cathode. Meanwhile, the lithium ions slip out of the graphite and zip through the electrolyte and the separator to the cathode, where they meet up with electrons that have made the journey through the circuit (see diagram below).
Nano to the rescue
Cui and colleagues have applied several nanotechnology-inspired solutions to keep silicon anodes from breaking down and to prevent battery-killing side reactions.
Graphite is today’s go-to anode material because it is highly conductive and thus readily passes collected electrons to the metal wires in a circuit. But graphite is only so-so at gathering lithium ions during charging. It takes six carbon atoms in graphite to hold on to a single lithium ion. That weak grip limits how much lithium the electrode can hold and thus how much power the battery can store.
Silicon has the potential to do far better. Each silicon atom can bind to four lithium ions. In principle, that means a silicon-based anode can store 10 times as much energy as one made from graphite. Electrochemists have struggled in vain for decades to tap that enormous capacity.
It’s easy enough to make anodes from chunks of silicon; the problem is that the anodes don’t last. As the battery is charged and lithium ions rush in to bind to silicon atoms, the anode material swells as much as 300%. Then, when the lithium ions rush out during the battery’s discharge cycle, the anode rapidly shrinks again. After only a few cycles of such torture, silicon electrodes fracture and eventually split into tiny, isolated grains. The anode—and the battery—crumbles and dies.
Cui thought he could solve the problem. His experience at Harvard and UC Berkeley had taught him that nanomaterials often behave differently from materials in bulk. For starters, they have a much higher percentage of their atoms at their surface relative to the number in their interior. And because surface atoms have fewer atomic neighbors locking them in place, they can move more easily in response to stresses and strains. Other types of atomic movement explain why thin sheets of aluminum foil or paper can bend without breaking more easily than chunks of aluminum metal or wood can.
In 2008, Cui thought that fashioning a silicon anode from nanosized silicon wires might alleviate the stress and strain that pulverize bulk silicon anodes. The strategy worked. In a paper in Nature Nanotechnology, Cui and colleagues showed that when lithium ions moved into and out of the silicon nanowires, the nanowires suffered little damage. Even after 10 repeated cycles of charging and discharging, the anode retained 75% of its theoretical energy storage capacity.
Unfortunately, silicon nanowires are much more difficult and expensive to fashion than bulk silicon. Cui and colleagues started devising ways to make cheaper silicon anodes. First, they found a way to craft lithium-ion battery anodes from spherical silicon nanoparticles. Though potentially cheaper, these faced a second problem: The shrinking and swelling of the nanoparticles as the lithium atoms moved in and out opened cracks in the glue that bound the nanoparticles together. The liquid electrolyte seeped between the particles, driving a chemical reaction that coated them in a non-conductive layer, known as a solid-electrolyte interphase (SEI), which eventually grew thick enough to disrupt the anode’s charge-collecting abilities. “It’s like scar tissue,” says Yuzhang Li, a graduate student in Cui’s lab.
A few years later, Cui and his colleagues hit on another nanotech solution. They created egg like nanoparticles, surrounding each of their tiny silicon nanoparticles—the yolk—with a highly conductive carbon shell through which lithium ions could readily pass. The shell gave silicon atoms in the yolk ample room to swell and shrink, while protecting them from the electrolyte—and the reactions that form an SEI layer. In a 2012 paper in Nano Letters, Cui’s team reported that after 1000 cycles of charging and discharging, their yolk-shell anode retained 74% of its capacity.
They did even better 2 years later. They assembled bunches of their yolk-shell nanoparticles into micrometer-scale collections resembling miniature pomegranates. Bunching the silicon spheres boosted the anode’s lithium storage capacity and reduced unwanted side reactions with the electrolyte. In a February 2014 issue of Nature Nanotechnology, the group reported that batteries based on the new material retained 97% of their original capacity after 1000 charge and discharge cycles.
Earlier this year, Cui and colleagues reported a solution that outdoes even their complex pomegranate assemblies. They simply hammered large silicon particles down to the micrometer scale and then wrapped them in thin carbon sheets made from graphene. The hammered particles wound up larger than the silicon spheres in the pomegranates—so big that they fractured after a few charging cycles. But the graphene wrapping prevented the electrolyte compounds from reaching the silicon. It was also flexible enough to maintain contact with the fractured particles and thus carry their charges to the metal wires. What’s more, the team reported in Nature Energy, the larger silicon particles packed more mass—and thus more power—into a given volume, and they were far cheaper and easier to make than the pomegranates. “He has really taken this work in the right direction,” Jun Liu says.
Powered by such ideas, Amprius has raised more than $100 million to commercialize lithium-ion batteries with silicon anodes. The company is already manufacturing cellphone batteries in China and has sold more than 1 million of them, says Song Han, the company’s chief technology officer. The batteries, based on simple silicon nanoparticles that are cheap to make, are only 10% better than today’s lithium-ion cells. But at Amprius’s headquarters, Han showed off nanowire-silicon prototypes that are 40% better. And those, he says, still represent only the beginning of how good silicon anodes will eventually become.
Now, Cui is looking beyond silicon. One focus is to make anodes out of pure lithium metal, which has long been viewed as the ultimate anode material, as it has the potential to store even more energy than silicon and is much lighter.
But there have been major problems here, too. For starters, an SEI layer normally forms around the lithium metal electrode. That’s actually good news in this case: Lithium ions can penetrate the layer, so the SEI acts as a protective film around the lithium anode. But as the battery cycles, the metal swells and shrinks just as silicon particles do, and the pulsing can break the SEI layer. Lithium ions can then pile up in the crack, causing a metal spike, known as a dendrite, to sprout from the electrode. “Those dendrites can pierce the battery separator and short-circuit the battery and cause it to catch fire,” says Yayuan Liu, another graduate student in Cui’s group.
Conventional approaches haven’t solved the problem. But nanotechnology might. In one approach to preventing dendrite formation, Cui’s team stabilizes the SEI layer by coating the anode with a layer of interconnected nanocarbon spheres. In another, they’ve created a new type of yolk-shell particle, made of gold nanoparticles inside much larger carbon shells. When the nanocapsules are fashioned into an anode, the gold attracts lithium ions; the shells give the lithium room to shrink and swell without cracking the SEI layer, so dendrites don’t form.
Improving anodes is only half the battle in making better batteries. Cui’s team has taken a similar nano inspired approach to improving cathode materials as well, in particular sulfur. Like silicon on the anode side, sulfur has long been seen as a tantalizing option for the cathode. Each sulfur atom can hold a pair of lithiums, making it possible in principle to boost energy storage several fold over conventional cathodes. Perhaps equally important, sulfur is dirt cheap. But it, too, has problems. Sulfur is a relatively modest electrical conductor, and it reacts with common electrolytes to form chemicals that can kill the batteries after a few cycles of charging and discharging. Sulfur cathodes also tend to hoard charges instead of giving them up during discharge.
Seeking a nanosolution, Cui’s team encased sulfur particles inside highly conductive titanium dioxide shells, boosting battery capacity fivefold over conventional designs and preventing sulfur byproducts from poisoning the cell. The researchers have also made sulfur-based versions of their pomegranates, and they have trapped sulfur inside long, thin nanofibers. These and other innovations have not only boosted battery capacity, but also raised a measure known as the coulombic efficiency—how well the battery releases its charges—from 86% to 99%. “Now, we have high capacity on both sides of the electrode,” Cui says.
Down the road, Cui says, he intends to put both of his key innovations together. By coupling silicon anodes with sulfur cathodes, he hopes to make cheap, high-capacity batteries that could change the way the world powers its devices. “We think if we can make it work, it will make a big impact,” Cui says.
It just might help him change the world, and get rich on the side.
Bio – Professor Yi Cui
Professor of Materials Science and Engineering, of Photon Science, Senior Fellow at the Precourt Institute for Energy and Prof, by courtesy, of Chemistry PhD, Harvard University (2002)
Cui studies nanoscale phenomena and their applications broadly defined. Research Interests: Nanocrystal and nanowire synthesis and self-assembly, electron transfer and transport in nanomaterials and at the nano interface, nanoscale electronic and photonic devices, batteries, solar cells, microbial fuel cells, water filters and chemical and biological sensors.
That company raised $26 million from Breakthrough Energy Ventures, Concord New Energy and Alfa Laval.
This makes for a solid record of successes for X. All threeactive projectsthat dealt primarily with energy have graduated from the lab.
Another energy concept, Project Foghorn, would have synthesized carbon-neutral fuel from seawater, but the teamdiscontinued the effortdue to the challenges of achieving cost-competitiveness with gasoline.
Cleantech investment rebound
The preliminary achievements of the three projects are all the more notable because groundbreaking energy hardware has been anathema to venture investment for years, since the big busts of the first cleantech investment boom.
Investors lost big with expensive bets on thin-film solar and biofuels, technologies which largely failed to overcome their mainstream alternatives.
Investor sentiments are changing, however. New strategic funds have emerged to offer a more direct line from energy startups to well-capitalized potential customers or buyers. Other funds have emerged targeting early-stage cleantech investment, including hardware.
Overall venture and private equity investment in cleantech for 2018 was the highest since 2010, according toBloomberg New Energy Finance. That total grew 127 percent over 2017.
“There’s both a wave of new innovation in this space that warrants investment, and capital largely available now for good ideas,” said Shayle Kann, senior VP of research and strategy at Energy Impact Partners, on arecent episodeofThe Interchange. “Rarely, I think, do we see at this point really good ideas with great teams that just can’t find capital to grow.”
Malta found capital despite theuninspiring track recordof technological alternatives to dominant lithium-ion batteries for energy storage.
Dandelion’s raise brings the company’s total funding to $23 million to make geothermal an attractive alternative to gas or oil heating in homes. It faces strong incumbents in a market where high costs have historically limited the penetration of geothermal.
“Dandelion Energy expects to use this round of funding to accelerate growth, invest in research and development, and expand its operations across New York state — opening new warehouses and growing its team,” the company said in the announcement.
Homebuilder Lennar joined the round, raising the possibility that it could include Dandelion systems in new-build homes.
Makani to benefit from Shell’s expertise
Of the three X cleantech graduates, Makani’s technology is the furthest from anything on the market. It’s developing a wind generator without the tower, by putting turbines on a drone kite that flies in circles while tethered to the ground. It has been testing a 600-kilowatt prototype in Hawaii.
If it reaches market, this design could drastically lower the cost of wind power and speed up deployment times, by eliminating heavy construction from wind farm development. It also opens up new territory that may be hard to reach with conventional designs.
Shell wants to help commercialize the kites for offshore deployment, where they could anchor to buoys in deep water with much less effort than it takes to secure a traditional floating turbine.
“We’ll be drawing on Shell’s extensive engineering and operational expertise with floating structures to make this transition,” Makani CEO Fort Felker wrote in ablog postWednesday.
The partners plan to test an offshore Makani system at theMarine Energy Test Centrein Norway later this year, and Felker added that he is working on other partnerships to assist commercialization.
Shell has invested heavily in the cleantech space over the last year, most recentlyacquiring Greenlotsto anchor electric mobility operations in North America.
The oil and gas supermajor separately invested in a different floating wind technology Wednesday.
Itacquired a 66 percent stakein the €18 million TetraSpar demonstration project, which will mount a 3.6-megawatt turbine 10 kilometers from the coast of Norway in waters 200 meters deep.
A researcher at Georgia Tech holds a perovskite-based solar cell, which is flexible and lighter than silicon-based versions. Credit: Rob Felt, Georgia Tech
There’s a lot to like about perovskite-based solar cells. They are simple and cheap to produce, offer flexibility that could unlock a wide new range of installation methods and places, and in recent years have reached energy efficiencies approaching those of traditional silicon-based cells.
But figuring out how to produce perovskite-based energy devices that last longer than a couple of months has been a challenge.
Now researchers from Georgia Institute of Technology, University of California San Diego and Massachusetts Institute of Technology have reported new findings about perovskite solar cells that could lead the way to devices that perform better.
“Perovskite solar cells offer a lot of potential advantages because they are extremely lightweight and can be made with flexible plastic substrates,” said Juan-Pablo Correa-Baena, an assistant professor in the Georgia Tech School of Materials Science and Engineering. “To be able to compete in the marketplace with silicon-based solar cells, however, they need to be more efficient.”
In a study that was published February 8 in the journal Science and was sponsored by the U.S Department Energy and the National Science Foundation, the researchers described in greater detail the mechanisms of how adding alkali metal to the traditional perovskites leads to better performance.
“Perovskites could really change the game in solar,” said David Fenning, a professor of nanoengineering at the University of California San Diego. “They have the potential to reduce costs without giving up performance. But there’s still a lot to learn fundamentally about these materials.”
To understand perovskite crystals, it’s helpful to think of its crystalline structure as a triad. One part of the triad is typically formed from the element lead. The second is typically made up of an organic component such as methylammonium, and the third is often comprised of other halides such as bromine and iodine.
In recent years, researchers have focused on testing different recipes to achieve better efficiencies, such as adding iodine and bromine to the lead component of the structure. Later, they tried substituting cesium and rubidium to the part of the perovskite typically occupied by organic molecules.
“We knew from earlier work that adding cesium and rubidium to a mixed bromine and iodine lead perovskite leads to better stability and higher performance,” Correa-Baena said.
But little was known about why adding those alkali metals improved performance of the perovskites.
To understand exactly why that seemed to work, the researchers used high-intensity X-ray mapping to examine the perovskites at the nanoscale.
“By looking at the composition within the perovskite material, we can see how each individual element plays a role in improving the performance of the device,” said Yanqi (Grace) Luo, a nanoengineering PhD student at UC San Diego.
They discovered that when the cesium and rubidium were added to the mixed bromine and iodine lead perovskite, it caused the bromine and iodine to mix together more homogeneously, resulting in up to 2 percent higher conversion efficiency than the materials without these additives.
“We found that uniformity in the chemistry and structure is what helps a perovskite solar cell operate at its fullest potential,” Fenning said. “Any heterogeneity in that backbone is like a weak link in the chain.”
Even so, the researchers also observed that while adding rubidium or cesium caused the bromine and iodine to become more homogenous, the halide metals themselves within their own cation remained fairly clustered, creating inactive “dead zones” in the solar cell that produce no current.
“This was surprising,” Fenning said. “Having these dead zones would typically kill a solar cell. In other materials, they act like black holes that suck in electrons from other regions and never let them go, so you lose current and voltage.
“But in these perovskites, we saw that the dead zones around rubidium and cesium weren’t too detrimental to solar cell performance, though there was some current loss,” Fenning said. “This shows how robust these materials are but also that there’s even more opportunity for improvement.”
The findings add to the understanding of how the perovskite-based devices work at the nanoscale and could lay the groundwork for future improvements.
“These materials promise to be very cost effective and high performing, which is pretty much what we need to make sure photovoltaic panels are deployed widely,” Correa-Baena said. “We want to try to offset issues of climate change, so the idea is to have photovoltaic cells that are as cheap as possible.”
That’s about how far UC Santa Barbara electrical and computer engineering professor John Bowers and his research team are reaching with the recent development of their mode-locked quantum dot lasers on silicon.
It’s technology that not only can massively increase the data transmission capacity of data centers, telecommunications companies and network hardware products to come, but do so with high stability, low noise and the energy efficiency of silicon photonics.
“The level of data traffic in the world is going up very, very fast,” said Bowers, co-author of a paper on the new technology in the journal Optica. Generally speaking, he explained, the transmission and data capacity of state-of-the-art telecommunications infrastructure must double roughly every two years to sustain high levels of performance. That means that even now, technology companies such as Intel and Cisco have to set their sights on the hardware of 2024 and beyond to stay competitive.
Enter the Bowers Group’s high-channel-count, 20 gigahertz, passively mode-locked quantum dot laser, directly grown — for the first time, to the group’s knowledge — on a silicon substrate. With a proven 4.1 terabit-per-second transmission capacity, it leaps an estimated full decade ahead from today’s best commercial standard for data transmission, which is currently reaching for 400 gigabits per second on Ethernet.
The technology is the latest high-performance candidate in an established technique called wavelength-division-multiplexing (WDM), which transmits numerous parallel signals over a single optical fiber using different wavelengths (colors). It has made possible the streaming and rapid data transfer we have come to rely on for our communications, entertainment and commerce.
The Bowers Group’s new technology takes advantage of several advances in telecommunications, photonics and materials with its quantum dot laser — a tiny, micron-sized light source — that can emit a broad range of light wavelengths over which data can be transmitted.
“We want more coherent wavelengths generated in one cheap light source,” said Songtao Liu, a postdoctoral researcher in the Bowers Group and lead author of the paper. “Quantum dots can offer you wide gain spectrum, and that’s why we can achieve a lot of channels.” Their quantum dot laser produces 64 channels, spaced at 20 GHz, and can be utilized as a transmitter to boost the system capacity.
The laser is passively ‘mode-locked’ — a technique that generates coherent optical ‘combs’ with fixed-channel spacing — to prevent noise from wavelength competition in the laser cavity and stabilize data transmission.
This technology represents a significant advance in the field of silicon electronic and photonic integrated circuits, in which the primary goal is to create components that use light (photons) and waveguides — unparalleled for data capacity and transmission speed as well as energy efficiency — alongside and even instead of electrons and wires. Silicon is a good material for the quality of light it can guide and preserve, and for the ease and low cost of its large-scale manufacture. However, it’s not so good for generating light.
“If you want to generate light efficiently, you want a direct band-gap semiconductor,” said Liu, referring to the ideal electronic structural property for light-emitting solids. “Silicon is an indirect band-gap semiconductor.” The Bowers Group’s quantum dot laser, grown on silicon molecule-by-molecule at UC Santa Barbara’s nanofabrication facilities, is a structure that takes advantage of the electronic properties of several semiconductor materials for performance and function (including their direct band-gaps), in addition to silicon’s own well-known optical and manufacturing benefits.
This quantum dot laser, and components like it, are expected to become the norm in telecommunications and data processing, as technology companies seek ways to improve their data capacity and transmission speeds.
“Data centers are now buying large amounts of silicon photonic transceivers,” Bowers pointed out. “And it went from nothing two years ago.”
Since Bowers a decade ago demonstrated the world’s first hybrid silicon laser (an effort in conjunction with Intel), the silicon photonics world has continued to create higher efficiency, higher performance technology while maintaining as small a footprint as possible, with an eye on mass production. The quantum dot laser on silicon, Bowers and Liu say, is state-of-the-art technology that delivers the superior performance that will be sought for future devices.
“We’re shooting far out there,” said Bowers, who holds the Fred Kavli Chair in Nanotechnology, “which is what university research should be doing.”
Research on this project was also conducted by Xinru Wu, Daehwan Jung, Justin Norman, MJ Kennedy, Hon K. Tsang and Arthur C. Gossard at UC Santa Barbara.
Researchers at ETH Zurich recently demonstrated that platinum nanoparticles can be used to kill liver cancer cells with greater selectivity than existing cancer drugs.
In recent years, the number of targeted cancer drugs has continued to rise. However, conventional chemotherapeutic agents still play an important role in cancer treatment. These include platinum-based cytotoxic agents that attack and kill cancer cells. But these agents also damage healthy tissue and cause severe side effects. Researchers at ETH Zurich have now identified an approach that allows for a more selective cancer treatment with drugs of this kind.
Platinum can be cytotoxic when oxidised to platinum(II) and occurs in this form in conventional platinum-based chemotherapeutics. Non-oxidised platinum(0), however, is far less toxic to cells. Based on this knowledge, a team led by Helma Wennemers, Professor at the Laboratory of Organic Chemistry, and Michal Shoshan, a postdoc in her group, looked for a way to introduce platinum(0) into the target cells, and only then for it to be oxidised to platinum(II). To this end, they used non-oxidised platinum nanoparticles, which first had to be stabilized with a peptide. They screened a library containing thousands of peptides to identify a peptide suitable for producing platinum nanoparticles (2.5 nanometres in diameter) that are stable for years.
Oxidised inside the cell
Tests with cancer cell cultures revealed that the platinum(0) nanoparticles penetrate into cells. Once inside the specific environment of liver cancer cells, they become oxidised, triggering the cytotoxic effect of platinum(II).
Studies with ten different types of human cells also showed that the toxicity of the peptide-coated nanoparticles was highly selective to liver cancer cells. They have the same toxic effect as Sorafenib, the most common drug used to treat primary liver tumours today. However, the nanoparticles are more selective than Sorafenib and significantly more so than the well-known chemotherapeutic Cisplatin. It is therefore conceivable that the nanoparticles will have fewer side effects than conventional medication.
Joining forces with ETH Professor Detlef Günther and his research group, Wennemers and her team were able to determine the platinum content inside the cells and their nuclei using special mass spectrometry. They concluded that the platinum content in the nuclei of liver cancer cells was significantly higher than, for instance, in colorectal cancer cells. The authors believe that the platinum(II) ions – produced by oxidation of the platinum nanoparticles in the liver cancer cells – enter the nucleus, and there release their toxicity.
“We are still a very long and uncertain way away from a new drug, but the research introduced a new approach to improve the selectivity of drugs for certain types of cancer – by using a selective activation process specific to a given cell type,” Wennemers says. Future research will expand the chemical properties of the nanoparticles to allow for greater control over their biological effects.
More information: Michal S. Shoshan et al. Peptide-Coated Platinum Nanoparticles with Selective Toxicity against Liver Cancer Cells, Angewandte Chemie International Edition (2018). DOI: 10.1002/anie.201813149
Scientists from ITMO in collaboration with international colleagues have proposed new DNA-based nanomachines that can be used for gene therapy for cancer. This new invention can greatly contribute to more effective and selective treatment of oncological diseases. The results were published in Angewandte Chemie.
Gene therapy is considered one of the promising ways of treating oncological diseases, even though the current approaches are far from perfect. Oftentimes, the agents fail to discern malignant cells from healthy ones, and are bad at interacting with folded RNA targets.
In order to solve this issue, scientists, including a Russian team from ITMO University headed by professor Dmitry Kolpashchikov, proposed special nanomachines. They sought to develop particular molecules, deoxyribozymes, which can interact with targeted RNA, bind them, unfold and cleave. According to the idea, these nanomachines have to recognize DNA oncomarkers and form complexes that can break down messenger RNA of vital genes with high selectivity, which will then result in apoptotic death of malignant cells.
The researchers tested the efficiency of the new machines in a model experiment and learned that they can cleave folded RNA molecules better than the original deoxyribozymes. They showed that the design of the nanomachine makes it possible to break down targeted RNA in the presence of a DNA oncomarker only, and the use of RNA-unfolding arms provides for better efficiency. The scientists also learned that the nanomachine can inhibit the growth of malignant cells, though cellular experiments didn’t show high specificity. The researchers associate this result with a possibly poor choice of the RNA target and a low stability of DNA structures in the cell.
The new approach differs fundamentally from the ones used before. The existing gene therapy agents are aimed at suppressing the expression of oncological markers. In the research in question, the scientists focused on the messenger RNA of vital genes, and the oncological marker was used as an activator. This makes it possible to apply the DNA nanomachine in treating any kind of cancer by using new DNA oncomarkers for activating the breakdown of targeted molecules.
The new invention opens new ways of treating oncological diseases. Still, there are many experiments to be conducted before it can be applied in therapy.
“For now, we are trying to introduce new functional elements in the framework that will contribute to a more effective recognition of oncological markers, and are also optimizing the DNA nanomachine for various RNA targets. In order to improve the efficiency and selectiveness of our constructions in cellular conditions, we are selecting new RNA targets and studying the stability of DNA machines in cells, which we plan to improve with the help of already existing chemical modifications,” comments Daria Nedorezova, Master’s student at ITMO University.
More information: Dmitry M Kolpashchikov et al, Towards DNA Nanomachines for Cancer Treatment: Achieving Selective and Efficient Cleavage of Folded RNA, Angewandte Chemie (2019). DOI: 10.1002/ange.201900829
Automotive startups always need to be viewed with a little caution, but as Jonny Smith (Fully Charged) discovers, Rivian have presented a very convincing launch. A large SUV and pick up truck at the LA motor show. Most impressive. (And probably why, Amazon and GM are considering investing in the EV SUV and Truck Start-Up – See Article Below)
Rivian is developing vehicles and technology to inspire people to get out and explore the world. These are their stories about the things they make, the places they go and the people they meet along the way.
Amazon, GM eye investment that would value Rivian at $1 billion to $2 billion, Reuters reports
Rivian Automotive, which plans to build the nation’s first electric pickup trucks along with SUVs in Normal, is in talks about an investment from Amazon and General Motors that would value the company at between $1 billion and $2 billion, Reuters reported Tuesday.
The two companies may receive minority stakes in the Plymouth, Mich.-based startup in a deal that could be concluded and announced this month, Reuters reported, citing sources that asked not to be identified because the matter is confidential.
The sources noted the talks may fail to reach a deal, Reuters reported. But the Chicago Tribune is reporting “talks are progressing” and a deal could be announced as soon as Friday, citing an unnamed source.
Amazon, General Motors and Rivian did not immediately respond to requests for comment from Reuters. Normal (Illinois) Mayor Chris Koos and Mike O’Grady, interim CEO of the Bloomington-Normal Economic Development Council, did not return calls seeking comment Tuesday night.
Rivian, which plans to hire as many as 1,000 employees to manufacture the “electric adventure” vehicles in the Twin Cities, unveiled a five-passenger pickup truck — the R1T — and the R1S SUV in November at the Los Angeles Auto Show. The vehicles are due in showrooms in late 2020.
“We’re launching Rivian with two vehicles that re-imagine the pickup and SUV segments,” Rivian founder and CEO R.J. Scaringe said in a statement at the time of the vehicles’ unveiling. “I started Rivian to deliver products that the world didn’t already have — to redefine expectations through the application of technology and innovation. Starting with a clean sheet, we have spent years developing the technology to deliver the ideal vehicle for active customers.”
The pickup, starting at $61,500, is expected to travel between 250 and 400 miles on a single charge, depending on the model, and is expected to tow up to 5,000 kilograms, or more than 11,000 pounds. The SUV, starting at around $70,000, can travel up to 400 miles on a single charge, said the company, and has a towing capacity of 3,500 kilograms.
The base models of each vehicle will reach 60 mph in 3 seconds, according to Rivian.
Rivian, which received performance-based incentives from state and local governments, paid $16 million for the former Mitsubishi Motors North America plant on Normal’s west side in 2017.
Town officials said in November that Rivian had already exceeded its benchmarks for a full property tax abatement at the plant for 2018, investing $10 million and employing 35 people. The plant had 60 workers at the time. Rivian had about 600 workers at the time across not only Normal but also facilities near Detroit, Los Angeles and San Francisco.
South Korea and Sweden are the most innovative countries in the world, according to a league table covering everything from the concentration of tech companies to the number of science and engineering graduates.
The index on innovative countries highlights South Korea’s position as the economy whose companies filed the most patents in 2017.
The electronics giant is South Korea’s most valuable company and has received more US patents than any company other than IBM since the start of the millennium. This innovation trickles down the supply chain and throughout South Korea’s economy.
The US dropped out of the top 10 in the 2018 Bloomberg Innovation Index, for the first time in the six years the gauge has been compiled.
Bloomberg attributed its fall to 11th place from ninth last year largely to an eight-spot slump in the rating of its tertiary education, which includes an assessment of the share of new science and engineering graduates in the labour force.
The US is now ranked 43 out of 50 nations for “tertiary efficiency”. Singapore and Iran take the top two spots.
The US’ ranking marks another setback for its higher education sector’s global standing in recent months: in September it was revealed neither of the world’s top two universities were considered to be American. Those honours went to theUK’s Oxford and Cambridge universitiesrespectively.
In addition to the US’ education slump in the innovation index, Bloomberg claims the country also lost ground when it came to value-added manufacturing. The country is now ranked in 23rd place, while Ireland and South Korea take the top two spots.
Despite these setbacks, the Bloomberg Innovation Index still ranks the US as number 1 when it comes to its density of tech companies.
The US is also second only to South Korea for patent activity.
These rankings may explain the disparity between Bloomberg’s list of innovative countries and the World Economic Forum’s own list of the10 most innovative economies.
Under this ranking, compiled as part of The Global Competitiveness Report 2017-2018, the US is listed as the second most innovative country in the world after Switzerland.
The US’ inclusion in this league table, and South Korea’s exclusion, are the two most notable differences between the different rankings.
Other than these nations, the majority of countries included in the top 10s are the same in both lists.
Tech titan Israel
One nation to feature prominently in both innovation rankings is Israel.
Taking third spot in the Global Competitiveness Report’s innovation league table, Israel is ranked 10th best country in the world for innovation overall by Bloomberg.
However, its index also ranks Israel as number 1 for two categories of innovation: R&D intensity and concentration of researchers.
Israel’s talent for research and development is illustrated by some of the major tech innovations to come out of the country.
These include the USB flash drive, the first Intel PC processor and Google’s Suggest function, to name just three.
It has about 4000 startups, and raises venture capital per capita at two-and-a-half times the rate of the US and 30 times that of Europe.
When it comes to being a world leader at innovation, it may simply be the case that you get out what you put in:according to OECD figures, Israel spends more money on research and development as a proportion of its economy than any other country – 4.3% of GDP against second-placed Korea’s 4.2%.
Switzerland is in third place spending 3.4% of its GDP on R&D, while Sweden spends 3.3%. The US spends just 2.8%.
Specific energy and specific power of rechargeable batteries. Specific energy is the capacity a battery can hold in watt-hours per kilogram (Wh/kg); specific power is the battery’s ability to deliver power in watts per kilogram (W/kg). (Source: Battery University)
” … a research team from Sichuan University in China and Clarkson University in the U.S. have discovered a key design rule for Li metal batteries: If you want to suppress dendrites, you have to use a defect-free host. More generally, carbon defects catalyze dendrite growth in metal anodes … “
Rechargeable lithium-ion (Li-ion) batteries are the dominant technology not only for portable electronics but it also is becoming the battery of choice for electric-vehicle and electric-grid energy-storage applications.
In a Li-ion battery, the cathode (positive electrode) is a lithium metal oxide while the anode (negative electrode) is graphite. But researchers are looking for ways to replace graphite with lithium metal as the anode to boost the battery’s energy density.
Lithium metal-based batteries such as Li–sulfur and Li–air batteries have received considerable attention because the packing density of lithium atoms is the highest in its metallic form and Li metal can store 10 times more energy than graphite.
However, there are safety and performance concerns for these types of batteries that arise from the formation of dendrites on the metal electrodes; an issue that has been known and investigated since the 1960s.
These dendrites form when metal ions accumulate on the surface of the battery’s electrodes as the electrode degrades during the charging process. Dendrites are often responsible for the highly publicized violent battery failures reported in the news.
When these branch-like filament deposits elongate until they penetrate the barrier between the two halves of the battery, they can cause electrical shorts, overheating and fires. They also cause significant cycling efficiency losses.
To avoid dendrites, researchers are experimenting with new battery electrolyte chemistries, new separator technologies, and new physical hosts for the lithium metal.
Carbon hosts, in particular, are very promising, since they may be added to the anode with little additional cost and minimal modification of the manufacturing process and they are becoming an important way to stabilize Li metal anodes.
However, there are seemingly contradictory findings reported in hundreds of prior publications on the subject: The hosts, which are predominantly made from various nanostructured carbons such as graphene, are in some cases very effective in eliminating dendrites. In other cases, they don’t work at all, or actually make the dendrite problem worse.
Up to now, design of such host systems has been largely Edisonian: researchers use a trial-and-error approach to find an architecture/structure that works better than the rest.
These findings address the major scientific problem of explaining how the structure and chemistry of the carbon per se affects dendrite growth.
Left half: Defect-free graphene protecting lithium metal anode from the electrolyte. Right half: Defective graphene catalyzing dendrite growth. (Source: Mitlin Research Group, Clarkson University)
“We discovered a critical and unexpected relationship between the host (graphene) chemical/structural defectiveness and its ability to suppress dendrites,” Prof. David Mitlin, who led the work, explains to Nanowerk. “To do this, we created what may be the world’s most pure and ordered graphene and compared it to a standard graphene based on reduced graphene oxide. Using such opposite materials, provided unique and fundamental insight into the way lithium dendrites form and grow.”
“The key finding, which will rationally guide future lithium battery design efforts, is that the carbon defects are themselves catalytic for dendrite growth,” Prof Wei Liu from Sichuan University’s Institute of New Energy and Low Carbon Technology, and the paper’s first author, points out. “Much of the ‘damage’ to the anode ultimately responsible for the dendrites occurs even before the battery is fully charged for the first time. Defects in the carbon host corrode the electrolyte at low voltages, leading to early dendrite formation.”
The team hypothesized that it was the host structure/chemistry that mattered, but needed to create ideal model systems to test the hypothesis.
Prof. Wei Liu’s unique Flow Assisted Sonication (FAS) approach allowed them to create nearly defect-free graphene. Literally, such oxygen-free and structural defect-free graphene has never been synthesized prior by a wet chemistry method.
This graphene is 1-3 atomic layers thick and with only about one and a half percent oxygen. This is much purer than the typical eight percent or more oxygen found in most graphene materials.
“It served as a perfect test bed to explore our hypothesis,” says Liu. “Without such a pristine structure, it would not have been possible to obtain the conclusive answers to the dendrite growth problem.”
He emphasizes that this in itself is a transformative accomplishment for the carbon and energy communities, since prior only vapor deposition could obtain such ideal defect-free structures.
The team then compared their defect-free graphene to a standard highly defective Hummers graphene baseline found in literature.
“A direct one-to-one comparison allowed us to obtain unique insight into the role of carbon defects on Li dendrite growth,” says Mitlin. “A critical new finding is that solid electrolyte interphase (SEI) formation occurring BEFORE metal plating actually dictates dendrites. The fate of the Li metal anode is in effect sealed once the carbon host forms SEI at the initial charge!”
Going forward, the researchers plan to commercialize defect-free graphene host materials for next- generation lithium batteries. They also plan to further understand the complex relationship between carbon defects and metal dendrites by examining carbons with tuned structure/chemistry for lithium, sodium and potassium batteries.